Renaming Animation Channels with a Script for dummies
No groups.
Going by screenshot.

The fcurves are not split into bone groups.

The bones have names &quot;mixamorig:LeftShoulder&quot; have renamed to &quot;Shoulder.L&quot; ie stripped out &quot;mixamorig:&quot; and then renamed.

Reinstated bone groups to new names. (optional)


Test script:. select rig, run script in object or pose mode. (As always back up first.)
import bpy

context = bpy.context
ob = context.object

def bonename(dp):
    #dp = fc.data_path
    if not dp.startswith(&quot;pose.bones&quot;):
        return None
    start = dp.find('[&quot;') + 2
    end = dp.find('&quot;]') 
    return dp[start : end]

def rename(name):
    if name.startswith(&quot;mixamorig:&quot;):
        name = name[10:]
    if name.startswith(&quot;Left&quot;):
        name = f&quot;{name[4:]}.L&quot;
    elif name.startswith(&quot;Right&quot;):
        name = f&quot;{name[5:]}.R&quot;
    return name
# test        
x = 'pose.bones[&quot;mixamorig:RightShoulder&quot;].location[0]'
print(rename(bonename(x)))

for pb in ob.pose.bones:
    pb.name = rename(pb.name)
    
action = ob.animation_data.action

for fc in action.fcurves:
    name = bonename(fc.data_path)
    if name:
        new_name = rename(name)
        fc.data_path.replace(name, new_name)
        if not fc.group:
            fc.group = (
                    action.groups.get(new_name) 
                    or
                    action.groups.new(new_name)
                    )